CVD methods and reactor devices have long been employed for depositing films of materials such as polycrystalline silicon, silicon dioxide (either doped or undoped), silicon nitride, etc. on selected substrates. Each of these materials may be deposited by a variety of techniques and for a variety of applications.
Generally, the material to be deposited is dependent upon selection of a reactant gas from which the material is deposited and various conditions of the process. A further discussion as to the chemistry of such deposition processes is not provided herein. Rather, it is merely noted that the CVD method and reactor device of the present invention are suitable for use with most materials contemplated for CVD applications.
A substantial number of CVD reactor designs have been employed in the past for carrying out such deposition techniques. These reactors are commonly characterized as providing a reaction chamber forming a controlled envelope or environment, preferably in terms of pressure and temperature, wherein position is initiated from a reactant gas onto a selected substrate.
As noted above, the reactant gas may include one or more gases taking part in the deposition process as well as inert gases which serve as background or carrier gases during the deposition process.
Additional details concerning the chemistry of such CVD processes are described for example in a copending and commonly assigned U.S. patent application entitled "Method of Depositing Silicon Dioxide Film and Product", and in many other references well known to those skilled in the CVD art.
In any event, it is important to understand that the selected CVD process is of critical importance in achieving uniformity of coating on the substrate, particularly where the substrate is a semiconductor wafer, for example. The importance of the CVD processes is even further emphasized by the need for precise definition on a one micron scale, where conformance of deposition is also of critical importance.
Prior CVD reactors tend to be capable of classification in a number of groups summarized immediately below.
"Horizontal systems" tend to be characterized by a holder for the substrate or wafers arranged for example in a tube with gas flowing through the tube to achieve deposition.
So-called "vertical systems" include a susceptor for holding wafers in a chamber typically formed by an inverted bell jar. The susceptor is typically rotated for achieving greater uniformity in coating across the surface of the wafers or substrate.
In "cylindrical or barrel systems", the substrates or wafers are typically placed in vertical alignment either on the inner or outer surface of a cylindrical susceptor. Typically, the susceptor is rotated within a chamber while reactant gases are introduced laterally to achieve deposition on the wafers.
Still other CVD reactors are characterized as "gas-blanketed downflow systems" wherein reactant gases are caused to flow downwardly through vertical channels while the substrates or wafers are arranged upon a holder or susceptor moving horizontally beneath the vertical channels to permit deposition from the gases.
It may generally be seen that CVD reactors of the types outlined above are also commonly characterized by means for regulating gas flow past the substrate during deposition. Timing and sequencing controls are also necessary and may vary in complexity to assure proper control of the deposition technique.
CVD reactors are also characterized by the need for effluent or exhaust means for removing unreacted gas and possibly carrier gas from the chamber as necessary.
CVD reactors which can generally be classified under one or more of the above types have been disclosed for example in U.S. Pat. Nos. 4,599,135; 4,596,208; 4,282,267; 4,142,004; 4,058,430; 3,922,467; 3,783,822; 3,757,733; 3,750,620; 3,696,779; 3,633,537; and 3,093,507.